TGF-β1 differentially modulates the collagen VI α5 and α6 chains in human tendon cultures

Collagen VI is a microfibrillar collagen with a potential regulatory role in tendon repair mechanism. We studied the expression of collagen VI α5 and α6 chains in normal human tendon fibroblast cultures, both under basal condition and in response to TGF-β1, a potent regulator of tendon healing. Under basal condition, we found that the α5 chain was expressed, although to a lesser extent with respect to the α3 chain; in contrast, the α6 chain was absent. The treatment with TGFβ1 induced an opposite effect on the expression of the α5 and α6 chains; in fact, while the α5 chain was dramatically reduced, the α6 chain was induced and released in the culture medium. These data indicate that collagen VI α5 and α6 chains are differentially involved in tendon matrix homeostasis. The α6 chain may represent a new potential biomarker for monitoring TGFβ1-related events in tendon, as healing and fibrotic scar formation.

Defective collagen VI α6 chain expression in the skeletal muscle of patients with collagen VI-related myopathies

Collagen VI is a non-fibrillar collagen present in the extracellular matrix (ECM) as a complex polymer; the mainly expressed form is composed of α1, α2 and α3 chains; mutations in genes encoding these chains cause myopathies known as Ullrich congenital muscular dystrophy (UCMD), Bethlem myopathy (BM) and myosclerosis myopathy (MM). The collagen VI α6 chain is a recently identified component of the ECM of the human skeletal muscle. Here we report that the α6 chain was dramatically reduced in skeletal muscle and muscle cell cultures of genetically characterized UCMD, BM and MM patients, independently of the clinical phenotype, the gene involved and the effect of the mutation on the expression of the “classical” α1α2α3 heterotrimer. By contrast, the collagen VI α6 chain was normally expressed or increased in the muscle of patients affected by other forms of muscular dystrophy, the overexpression matching with areas of increased fibrosis. In vitro treatment with TGF-β1, a potent collagen inducer, promoted the collagen VI α6 chain deposition in the ECM of normal muscle cells, whereas, in cultures derived from collagen VI-related myopathy patients, the collagen VI α6 chain failed to develop a network outside the cells and accumulated in the endoplasmic reticulum. The defect of the α6 chain points to a contribution to the pathogenesis of collagen VI-related disorders.

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Collagen VI is an ECM component of the human skeletal muscle.

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We evaluated the α6 chain in collagen VI-related and other muscular dystrophies.

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The α6 chain was reduced in collagen VI-related diseases but not in other myopathies.

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A correlation between the α6 chain and fibrosis was demonstrated in MDC1A.

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The α6 chain is involved in the pathogenesis of collagen VI diseases and fibrosis.

Myeloma cells suppress osteoblasts through sclerostin secretion

Wingless-type (Wnt) signaling through the secretion of Wnt inhibitors Dickkopf1, soluble frizzled-related protein-2 and -3 has a key role in the decreased osteoblast (OB) activity associated with multiple myeloma (MM) bone disease. We provide evidence that another Wnt antagonist, sclerostin, an osteocyte-expressed negative regulator of bone formation, is expressed by myeloma cells, that is, human myeloma cell lines (HMCLs) and plasma cells (CD138+ cells) obtained from the bone marrow (BM) of a large number of MM patients with bone disease. We demonstrated that BM stromal cells (BMSCs), differentiated into OBs and co-cultured with HMCLs showed, compared with BMSCs alone, reduced expression of major osteoblastic-specific proteins, decreased mineralized nodule formation and attenuated the expression of members of the activator protein 1 transcription factor family (Fra-1, Fra-2 and Jun-D). Moreover, in the same co-culture system, the addition of neutralizing anti-sclerostin antibodies restored OB functions by inducing nuclear accumulation of β-catenin. We further demonstrated that the upregulation of receptor activator of nuclear factor κ-B ligand and the downregulation of osteoprotegerin in OBs were also sclerostin mediated. Our data indicated that sclerostin secretion by myeloma cells contribute to the suppression of bone formation in the osteolytic bone disease associated to MM.

Osteoblast apoptosis in periodontal disease: role of TNF-related apoptosis-inducing ligand

Periodontal disease (Pd) is characterized by an increased osteoclast resorption and a decreased osteoblast (OB) bone formation. OBs obtained from alveolar bone of Periodontitis patients (Pp) undergo apoptosis in the presence of TNF-related apoptosis-inducing ligand (TRAIL). We studied the intracellular apoptotic pathway induced by TRAIL; TRAIL death (DR4, DR5) and decoy (DcR1, DcR2) receptors expression in Periodontitis patients OBs (PpOBs), and we measured the concentration of TRAIL in the serum of Pp. We demonstrated that DNA fragmentation and activation of caspase-8 and caspase-3 in PpOBs, following TRAIL stimulation, occurred in shorter time; moreover, a higher amount of both caspases was activated in order to direct OBs. Down-regulation of DcR2 in PpOBs was demonstrated and high TRAIL levels were detected in the serum of Pp. In conclusion, our data suggest that PpOBs are more sensitive to TRAIL-induced apoptosis when compared to the control group. The down-regulation of DcR2 possibly leads to an imbalanced ratio between death and decoy receptors. Our findings highlight a role of TRAIL in the pathogenesis of Pd.